/**
 * 2009-5-7
 */
package name.katlog.zlex.chapter08_3ElGamal;

import static org.junit.Assert.*;

import java.security.AlgorithmParameterGenerator;
import java.security.AlgorithmParameters;
import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;
import javax.crypto.spec.DHParameterSpec;

import org.apache.commons.codec.binary.Base64;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.junit.Before;
import org.junit.Test;

/**
 * ElGamal校验
 * 
 * @author 梁栋
 * @version 1.0
 */
public class ElGamalCoderTest {
	
	static  class ElGamalCoder {

		/**
		 * 非对称加密密钥算法
		 */
		public static final String KEY_ALGORITHM = "ElGamal";

		/**
		 * 密钥长度
		 * 
		 * ElGamal算法默认密钥长度为1024 
		 * 密钥长度范围在160位至16,384位不等。
		 */
		private static final int KEY_SIZE = 256;

		/**
		 * 公钥
		 */
		private static final String PUBLIC_KEY = "ElGamalPublicKey";

		/**
		 * 私钥
		 */
		private static final String PRIVATE_KEY = "ElGamalPrivateKey";

		/**
		 * 用私钥解密
		 * 
		 * @param data
		 *            待解密数据
		 * @param key
		 *            私钥
		 * @return byte[] 解密数据
		 * @throws Exception
		 */
		public static byte[] decryptByPrivateKey(byte[] data, byte[] key)
				throws Exception {

			// 加入BouncyCastleProvider支持
			Security.addProvider(new BouncyCastleProvider());

			// 私钥材料转换
			PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(key);

			// 实例化密钥工厂
			KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);

			// 生成私钥
			Key privateKey = keyFactory.generatePrivate(pkcs8KeySpec);

			// 对数据解密
			Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());

			cipher.init(Cipher.DECRYPT_MODE, privateKey);

			return cipher.doFinal(data);
		}

		/**
		 * 用公钥加密
		 * 
		 * @param data
		 *            待加密数据
		 * @param key
		 *            公钥
		 * @return byte[] 加密数据
		 * @throws Exception
		 */
		public static byte[] encryptByPublicKey(byte[] data, byte[] key)
				throws Exception {

			// 加入BouncyCastleProvider支持
			Security.addProvider(new BouncyCastleProvider());

			// 公钥材料转换
			X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(key);

			// 实例化密钥工厂
			KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);

			// 生成公钥
			Key publicKey = keyFactory.generatePublic(x509KeySpec);

			// 对数据加密
			Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());

			cipher.init(Cipher.ENCRYPT_MODE, publicKey);

			return cipher.doFinal(data);
		}

		/**
		 * 生成密钥
		 * 
		 * @return Map 密钥Map
		 * @throws Exception
		 */
		public static Map<String, Object> initKey() throws Exception {

			// 加入BouncyCastleProvider支持
			Security.addProvider(new BouncyCastleProvider());

			// 实例化算法参数生成器
			AlgorithmParameterGenerator apg = AlgorithmParameterGenerator
					.getInstance(KEY_ALGORITHM);

			// 初始化算法参数生成器
			apg.init(KEY_SIZE);

			// 生成算法参数
			AlgorithmParameters params = apg.generateParameters();

			// 构建参数材料
			DHParameterSpec elParams = (DHParameterSpec) params
					.getParameterSpec(DHParameterSpec.class);

			// 实例化密钥对儿生成器
			KeyPairGenerator kpg = KeyPairGenerator.getInstance(KEY_ALGORITHM);

			// 初始化密钥对儿生成器
			kpg.initialize(elParams, new SecureRandom());

			// 生成密钥对儿
			KeyPair keys = kpg.genKeyPair();

			// 取得密钥
			PublicKey publicKey = keys.getPublic();

			PrivateKey privateKey = keys.getPrivate();

			// 封装密钥
			Map<String, Object> map = new HashMap<String, Object>(2);

			map.put(PUBLIC_KEY, publicKey);

			map.put(PRIVATE_KEY, privateKey);

			return map;
		}

		/**
		 * 取得私钥
		 * 
		 * @param keyMap
		 *            密钥Map
		 * @return byte[] 私钥
		 * @throws Exception
		 */
		public static byte[] getPrivateKey(Map<String, Object> keyMap)
				throws Exception {

			Key key = (Key) keyMap.get(PRIVATE_KEY);

			return key.getEncoded();
		}

		/**
		 * 取得公钥
		 * 
		 * @param keyMap
		 * @return
		 * @throws Exception
		 */
		public static byte[] getPublicKey(Map<String, Object> keyMap)
				throws Exception {

			Key key = (Key) keyMap.get(PUBLIC_KEY);

			return key.getEncoded();
		}
	}

	/**
	 * 公钥
	 */
	private byte[] publicKey;

	/**
	 * 私钥
	 */
	private byte[] privateKey;

	/**
	 * 初始化密钥
	 * 
	 * @throws Exception
	 */
	@Before
	public void initKey() throws Exception {
		
		Map<String, Object> keyMap = ElGamalCoder.initKey();

		publicKey = ElGamalCoder.getPublicKey(keyMap);
		privateKey = ElGamalCoder.getPrivateKey(keyMap);

		System.err.println("公钥: \n" + Base64.encodeBase64String(publicKey));
		System.err.println("私钥： \n" + Base64.encodeBase64String(privateKey));
	}

	/**
	 * 校验
	 * 
	 * @throws Exception
	 */
	@Test
	public void test() throws Exception {

		String inputStr = "ElGamal加密";

		byte[] data = inputStr.getBytes();

		System.err.println("原文: \n" + inputStr);

		byte[] encodedData = ElGamalCoder.encryptByPublicKey(data, publicKey);

		System.err.println("加密后: \n" + Base64.encodeBase64String(encodedData));

		byte[] decodedData = ElGamalCoder.decryptByPrivateKey(encodedData,
				privateKey);

		String outputStr = new String(decodedData);

		System.err.println("解密后: \n" + outputStr);

		assertEquals(inputStr, outputStr);
	}

}
